The present invention relates to a method and apparatus for securing to one another two structural elements while maintaining a gap between them and, more specifically, to an apparatus for fastening the oil pan to the engine block of a tractor.
It is common to use so-called structural engines in agricultural vehicles, such as tractors, where the engine block forms part of the unsprung mass (or chassis) of the vehicle and is relied upon to assure the structural rigidity of the tractor. To increase the rigidity of such an engine, it is known to secure a substantial oil pan to the underside of the engine block. The oil pan is not only secured to the engine block to collect the lubricating oil circulating through the engine but also acts as a structural element onto which other elements of the tractor chassis such as the front support or the transmission are bolted.
In this situation, because of tolerance stack-up in the manufacture of the engine block, the oil pan and the front support, it is not possible to ensure that the rear face of the front support will always simultaneously lie flush with both the front face of the engine block and the front face of the oil pan. These three elements are therefore intentionally dimensioned such that a gap will always be present between the front support and the oil pan, though the size of the gap may vary from one engine to another.
Conventionally, this gap is taken up by the use of shims, i.e. thin metal spacers that are sandwiched in the gap between the front support and the oil pan before these two are bolted to one another. It is important to select shims of the correct thickness to take up the gap but it is found in practice that incorrect shims are sometimes selected and this results in damage because of the increased stress placed on the elements. It is also time consuming to select and mount the shims and this adds to the manufacturing costs.
In U.S. Pat. No. 4,108,407, an adjustment device is shown in which the use of shims is avoided by providing an externally threaded adjustment member projecting from a bore in a support member. The adjustment member is turned until the gap between the support and a slightly offset tool assembly is taken up, whereafter the adjustment member is locked in place by a locking nut. To secure the support and the tool assembly together, a screw is inserted through a central bore in the adjustment member and tightened with a predetermined torque. In practice, it is not only found that such a system is expensive to manufacture but also that it is time consuming to properly adjust the adjustment member.
The present invention therefore seeks to provide a method and the means of bolting elements to one another while maintaining a spacing between them, which dispenses with the use of shims or threaded adjustment devices and allows simple, swift and reliable bolting of the elements to one another.
In accordance with a first aspect of the present invention, there is provided a method of bolting to one another two structural elements while maintaining a spacing between the two elements.
The method is characterized in that it comprises the steps of:
forming a through bore in a first element;
placing a sliding annular bush within the bore of the first element to project from the first element into contact with the surface of the second element;
locking the bush in relation to the bore in the first element; and
securing the structural elements to one another by means of a bolt passing through the annular bush.
The steps of the method need not be carried out in the above sequence as it is possible to lock the bush to the bore after securing the structural elements to one another. In a preferred embodiment of the invention, the bush is slidable in the bore in the first element and is locked relative to the bore by means of an anaerobic adhesive.
It is alternatively possible for the bush to be a shrink-fit in the bore. In this case, the bush would be an interference fit when the temperature of the bush is the same as that of the bore but it would be slidable in the bore when it is significantly colder, for example if it is submerged in liquid nitrogen prior to assembly.
As an alternative to the use of an anaerobic adhesive, the bush may be mechanically locked in place. This can be achieved by the use of a pinch bolt or by the use of one or more sliding wedges that expand the diameter of the bush during assembly.
It is advantageous to knurl the outer surface of the bush and to case harden it so that it should remain in place during the setting of the adhesive.
It has been found that anaerobic adhesives that are currently commercially available, such as Loctite RC640, can achieve a permanent joint between the bush and the bore capable of withstanding the forces on the bush during normal operation of the structural elements.
In accordance with a second aspect of the present invention, there is provided an assembly comprising a first, a second and a third element, each element being secured to the other two elements, the first element mating flush with the face of the third element but there being a gap of indeterminate width between the surfaces of the first and second elements.
The assembly is characterized in that the first element is secured to the second element while maintaining the spacing between the first and second elements by means of a bolt passing through a sliding annular bush adjustably received in a bore in the first element, the bush being locked relative to the bore after it has been positioned to bridge the gap between the first and second elements.
The invention will be described below with reference to an embodiment in which the first element is a front support of an agricultural tractor, the second element is an oil pan and the third element is an engine block. It will be appreciated however that the invention can be applied to the bolting together of any two elements that are spaced apart when it is desired not to close the gap between the elements.